LibJS: Make Cell::initialize() return void

Stop worrying about tiny OOMs.

Work towards #20405

Userland/Libraries/LibWeb/HTML/HTMLFrameElement.h

@@ -20,7 +20,7 @@ public:
 private:
     HTMLFrameElement(DOM::Document&, DOM::QualifiedName);
 
-    virtual JS::ThrowCompletionOr<void> initialize(JS::Realm&) override;
+    virtual void initialize(JS::Realm&) override;
 
     // ^DOM::Element
     virtual i32 default_tab_index_value() const override;